This invention relates to carburetors and more particularly to apparatus for venting fuel vapors from the fuel bowl of a carburetor.
Carburetor assemblies typically include a fuel bowl which holds fuel, e. g. gasoline, that is supplied to the engine on which the carburetor is installed. The gasoline gives off vapors some of which are heavier and some of which are lighter than air. The presence of these vapors in the fuel bowl creates an internal bowl pressure which may force fuel out of the fuel bowl and into the air passage where the air/fuel mixture combusted in the engine is produced thereby making precise fuel metering difficult and causing an overly rich air/fuel mixture to be produced. Conventionally, the heavier than air vapors are drawn off from the fuel bowl to, for example, a charcoal canister where they condense. The lighter than air vapors, meanwhile, are vented from the fuel bowl to an air cleaner mounted adjacent the carburetor or to the space between the air cleaner and the carburetor's air inlet. By venting the fuel vapors from the fuel bowl, the pressure in the fuel bowl is balanced with the outside air pressure and fuel metering is precisely maintained. However, the venting of the lighter than air vapors is usually continuous and, when the engine is off, the vapors eventually saturate the air cleaner or the space between the cleaner and the air inlet. Further, these vapors gravitate into the carburetor's air horn and the intake manifold of the engine and may displace the air in these regions. Consequently, when the engine is next started, an overly rich air/fuel mixture is supplied to the engine which not only makes the engine difficult to start, but also increases the amount of pollutants emitted from the engine during starting.